1. Technical Field
The present invention relates to motor drive devices that use a PWM (Pulse Width Modulation) control method, and in particular, to a motor drive device for performing abnormal determination based on an application voltage value and an actual measurement voltage value of the motor.
2. Related Art
In an electric power steering device of a vehicle, an electric motor such as a three-phase brushless motor is arranged to provide a steering auxiliary force corresponding to steering torque of a handle to a steering mechanism. A motor drive device by the PWM control method is known as a device for driving the motor (e.g., Japanese Unexamined Patent Publication No. 2007-244133).
The motor drive device of the PWM control method includes an inverter circuit in which three pairs of upper and lower arms having a switching element on the upper arm and the lower arm are arranged. The inverter circuit receives a PWM signal for turning ON/OFF each of the switching elements. The PWM signal is generated based on a deviation of a current command value (target value) of a motor corresponding to steering torque detected by a torque sensor and an actual measurement value of the current actually flowing to the motor. The motor is driven by individually providing six types of PWM signals having a predetermined duty to six switching elements of the inverter circuit and turning ON/OFF each of the elements.
In such a motor drive device, the output torque of the motor becomes abnormal when failure occurs in the circuit or the motor, and the desired steering auxiliary force may not be obtained. Therefore, there has been proposed a motor drive device having a failure detection function of comparing the application voltage value and the actual measurement voltage value of the motor, and determining as abnormal if the difference is greater than or equal to a predetermined value (e.g., Japanese Patent No. 3812739).